Generally in a case where an abnormal current flows due to failure of a load of a device such as a short circuit, the load and a power source are protected by a method of cutting a power source by detecting the abnormal current or that of inserting a fuse which is flown by an abnormal current between the power source and the load. More than 100 pieces of discharge tubes are used to connect to an AC power source in an ozone generating device of a large capacity. In the ozone generating device having the above-mentioned configuration, due to the variation of discharge tubes, short-circuit discharge is generated in one piece of discharge tubes, and arc discharge may be generated in the discharge tube. In occurrence of the above-mentioned abnormality, in order to protect other loads and a power source, or to continue the operation, various kinds of technologies have been proposed.
For example, in an ozone generating device comprising a plurality of discharging elements, in a case where one or a plurality of discharging elements become abnormal in operation, the abnormality of the discharging element is detected by each abnormality detecting means which is connected to each discharging element, and then the output power of ac power circuit is decreased to a predetermined output power value. As a result, the electric current as to be overloaded to the other normal discharging elements does not flow after electrically separating the discharging element having the abnormality, and thereby the normal discharging elements are prevented from being destroyed in succession and the operation is continued by the remaining discharging elements without interrupting the generation of the ozone. (Patent Document 1)
Further in an ozone generating device comprising a discharging tube comprising a glass tube wherein the discharging tube is connected to an output of an inverter, when an abnormality is generated, such as breakage of a glass tube, an output circuit at a first voltage V1 which outputs a voltage drop with a first time constant and an output circuit at a second voltage V2 which outputs a voltage drop with a second time constant slower than the first time constant are equipped and a comparator which is connected to the above circuits outputs an abnormality occurrence signal when the second voltage V2 is higher than the first voltage V1. (Patent Document 2)